The interactions between epithelial and muscular cells of tracheal wall were studied by a mechanographic technique in rats of different ages. The state of the epithelium was assessed using hematoxylin-eosin stained sections. The epithelium-dependent relaxation was tound to be most pronounced in 10-12-week-old rats. It was not observed in younger rats probably due to the low sensitivity of guanylate cyclase to activating stimuli. Destructive changes in the respiratory epithelium after 24 weeks of life reduced the amplitude of epithelium-dependent relaxation in old rats.

A mechanographic study of contractile responses by tracheal smooth muscle segments of rats to a histaminergic agent showed that intact segments did not respond to histamine in the concentrations used (0.01-10 rtM), whereas depolarized segments responded to histamine by dose-dependent contractions which were considerably enhanced following mechanical removal of the tracheal epithelium. Key Words: trachea; smooth muscle; histamineHeightened reactivity of the bronchi is an important pathogenic mechanism of obstructive lung disease [9][10][11]. Among the mediators of bronchospasm, a leading role is played by histamine. Activation of histamine receptors results in the exit of calcium to the cytosol and in muscular contraction. This is a characteristic feature of bronchial smooth muscle cells (SMC) in rabbits and guinea pigs [5,9], in which bronchospastic responses of allergic or inflammatory origin are readily inducible [6].In rats, however, it is virtually impossible to produce bronchospasm by any means. This phenomenon has attracted the attention of many investigators, but has not received a uniquely interpretable explanation [6,9,11].We focused on the observation that tracheal SMC do not respond by contraction to histamine in either physiological or supraphysiological concentrations [5], even though histamine receptors are abundant on the membranes of these ceils.The purpose of the present study was to examine the mechanisms responsible for the resistance of rat tracheal SMC to histaminergic agents. Department of Biophysics, Siberian Medical University, Tomsk MATERIALS AND METHODSCircular segments 3-4 mm wide prepared from the lower parts of tracheas of random-bred male rats were placed in a thermostatically controlled chamber containing a continuously aerated Krebs solution of the following composition (mM): 120.4 NaC1, 5.0 KC1, 1.2 MgCI=, 2.5 CaCI~, 1.2 NaH=PO 4, 15.5 HEPES, and 11.5 glucose (pH 7.35, 37~ This solution was changed every 10 min. In some rats, the tracheal epithelium was removed mechanically [12]. Contractile activity was recorded with a mechanotron under near-isometric conditions. Mechanical tension was estimated in percent of the contractile response to a hyperpotassic (40 mM KC1) Krebs solution. RESULTSThe first series of tests was designed to assess the effect of histamine on the tracheal segments. As shown in Fig. 1, these segments failed to respond to histamine in concentrations of 0.01 to 10 ~tM, but did respond in a dose-dependent manner when 40 mM KC1 were present in the solution. The

The contribution of calmodulin and protein kinase C to the regulation of epithelial relaxing factor production by the tracheal epithelium and the role of adenylate and guanylate cyclase in the realization of the effect of this factor on airway smooth muscles are studied by the mechanographic method with cascade perfusion. Calmodulin and protein kinase C are shown to participate in the production of relaxing factor by epitheliocytes, guanylate cyclase being the principal target in exposure of smooth muscles to epithelial relaxing factor. Key Words: epithelium; trachea; smooth muscles; contractionRecent studies have confirmed the capacity of airway epithelium to modulate the contractile reactions of smooth muscles [4,8,10]. By analogy with the function of vascular epithelium, the mechanism of the modulating effect may be related to the production of epithelial relaxing factor (ERF). Available data permit a general description of the mechanism of epithelial regulation of the contractility of vascular smooth muscles [3], but this concept evidently cannot be extrapolated to the epithelial-smooth muscle relationships in the airways. Specifically, the mechanisms of calcium-dependent regulation of ERF production are unknown. The type and role of interactions between the adenylate and guanylate cyclase signal systems in the course of epithelium-induced bronchial dilatation also require elucidation.In this research we studied the contribution of calmodulin (CM) and protein kinase C to the regulation of ERF production by tracheal epithelium and the role of adenylate and guanylate cyclase in the realization of the effect of ERF on the muscles of the airways.Siberian Medical University, Tomsk MATERIALS AND METHODSRing segments 3-4 mm wide and a 30-ram-long tubular preparation were cut from the trachea of outbred male white rats. The segment intended as the "acceptor" was mechanically deepithelialized as described previously [5]. The preparations were placed in a device for cascade perfusion [3]. Aerated Krebs' solution was delivered to the ERF "aeceptor" at a rate of 0.5 ml/min through the lumen of the tracheal tubular preparation (ERF "donor"). The mechanical tension of the "acceptor" was measured using a 6MX2B mechanotron under conditions approaching isometric.Calcium ionophore (A23187, 0.5 ~tM), added to Krebs' solution perfused through the "donor" lumen, initiated the production of ERF. The effects of ERF on the "acceptor" were assessed as the percent share of mechanical tension reduction in response to perfusion of hyperpotassium (30 mM) Krebs' solution. Krebs' solution of the following composition (mM) was used in the study: 120.4 NaC1, 5.9 KC1, 1.2 MgC12, 2.5 CaCI~, 1.2 NaH2PO4, 15.5 NaHCO3, and 11.5 glucose, pH 7.35 at 37~The test solutions were based on

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